U.S. Pat. No. 4,768,347, assigned to the assignee hereof, discloses a refrigerant recovery system that includes a compressor having an inlet coupled through an evaporator and through a solenoid valve to the refrigeration equipment from which refrigerant is to be withdrawn, and an outlet coupled through a condenser to a refrigerant storage container or tank. The evaporator and condenser are contained within a closed cylindrical canister for heat exchange and oil separation, the canister having an oil drain in the bottom. The refrigerant storage container is carried by a scale having a limit switch coupled to control electronics to prevent or terminate further refrigerant recovery when the container is full. The scale comprises a platform pivotally mounted by a hinge pin to a wheeled cart, which also carries the evaporator/condenser unit, compressor, control electronics and associated valves and hoses.
U.S. Pat. No. 4,805,416, also assigned to the assignee hereof, discloses systems for recovering, purifying and recharging refrigerant in which, during a purification cycle, refrigerant is circulated from the refrigerant storage container in a closed path through a circulation valve and a filter for removing water and other contaminants, and then returned to the container. U.S. application Ser. No. 263,887, filed Oct. 28, 1988 and also assigned to the assignee hereof, discloses a refrigerant recovery system that includes a refrigerant storage container, refrigeration circuitry for withdrawing refrigerant from equipment under service and feeding such refrigerant to the container for storage, and a scale supporting the container for sensing impending overfill of the container. The scale includes a beam horizontally rigidly cantilevered from a base. A switch is positioned adjacent to the cantilever-remote end of the beam, and is responsive to resilient deflection of the beam to indicate impending overfill of the container and prevent or terminate operation or the refrigerant recovery system.
A problem with refrigeration service devices of the subject character lies in potential entrapment of air in the air conditioning system being serviced. All refrigerants, including R-12 (dichlorodifluoromethane), have characteristic saturation pressures that vary as associated functions of temperature as long as refrigerant is present in both liquid and vapor phases, such as in the refillable storage container of a refrigerant recovery, purification and/or recharging station. If air is present in the system or container, a differential pressure above the saturation pressure is created, which is proportional to the quantity of air. However, absorption of air is undesirable in an air conditioning system in that it displaces cooling capacity, causes higher operating temperatures and pressures, and reduces operating life of compressor components. Automotive vehicle manufacturers have set a limit on the amount of air permissible in a refillable storage container after recovery and recycling (such as through a filter/dryer) and prior to recharging into a vehicle. Commercial air conditioning and refrigeration system manufacturers are expected to establish similar limits.
It is therefore a general object of the present invention to provide a refrigerant handling system and method that include facility for purging trapped air from the system. A more specific object of the invention is to provide a system and method for circulating liquid refrigerant to a storage container that include facility for automatically purging air from within the container when the differential air pressure within the container exceeds saturation pressure of refrigerant within the system by more than a preselected threshold. Yet another and more specific object of the invention is to provide a liquid refrigerant purification system that includes a refrigerant storage container, a pump coupled to the container for circulating liquid refrigerant from the container through a filter/dryer and then returning the refrigerant to the container, and a purging valve for automatically venting air from the container when the air/saturation pressure differential exceeds a prespecified threshold.